/* pngrio.c - functions for data input

  libpng 1.2.7 - September 12, 2004
  For conditions of distribution and use, see copyright notice in png.h
  Copyright (c) 1998-2004 Glenn Randers-Pehrson
  (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)

  This file provides a location for all input.  Users who need
  special handling are expected to write a function that has the same
  arguments as this and performs a similar function, but that possibly
  has a different input method.  Note that you shouldn't change this
  function, but rather write a replacement function and then make
  libpng use it at run time with png_set_read_fn(...).
*/

#define PNG_INTERNAL
#include "png.h"

/* Read the data from whatever input you are using.  The default routine
    reads from a file pointer.  Note that this routine sometimes gets called
    with very small lengths, so you should implement some kind of simple
    buffering if you are using unbuffered reads.  This should never be asked
    to read more then 64K on a 16 bit machine. */
void /* PRIVATE */
png_read_data( png_structp png_ptr, png_bytep data, png_size_t length ) {
  png_debug1( 4, "reading %d bytes\n", ( int )length );
  if( png_ptr->read_data_fn != NULL ) {
    ( *( png_ptr->read_data_fn ) )( png_ptr, data, length );
  } else
  { png_error( png_ptr, "Call to NULL read function" ); }
}

#if !defined(PNG_NO_STDIO)
/* This is the function that does the actual reading of data.  If you are
  not reading from a standard C stream, you should create a replacement
  read_data function and use it at run time with png_set_read_fn(), rather
  than changing the library. */
#ifndef USE_FAR_KEYWORD
void PNGAPI
png_default_read_data( png_structp png_ptr, png_bytep data, png_size_t length ) {
  png_size_t check;
  /* fread() returns 0 on error, so it is OK to store this in a png_size_t
    instead of an int, which is what fread() actually returns.
  */
  #if defined(_WIN32_WCE)
  if( !ReadFile( ( HANDLE )( png_ptr->io_ptr ), data, length, &check, NULL ) ) {
    check = 0;
  }
  #else
  check = ( png_size_t )fread( data, ( png_size_t )1, length,
                               ( png_FILE_p )png_ptr->io_ptr );
  #endif
  if( check != length ) {
    png_error( png_ptr, "Read Error" );
  }
}
#else
/* this is the model-independent version. Since the standard I/O library
  can't handle far buffers in the medium and small models, we have to copy
  the data.
*/

#define NEAR_BUF_SIZE 1024
#define MIN(a,b) (a <= b ? a : b)

static void /* PRIVATE */
png_default_read_data( png_structp png_ptr, png_bytep data, png_size_t length ) {
  int check;
  png_byte *n_data;
  png_FILE_p io_ptr;
  /* Check if data really is near. If so, use usual code. */
  n_data = ( png_byte * )CVT_PTR_NOCHECK( data );
  io_ptr = ( png_FILE_p )CVT_PTR( png_ptr->io_ptr );
  if( ( png_bytep )n_data == data ) {
    #if defined(_WIN32_WCE)
    if( !ReadFile( ( HANDLE )( png_ptr->io_ptr ), data, length, &check, NULL ) ) {
      check = 0;
    }
    #else
    check = fread( n_data, 1, length, io_ptr );
    #endif
  } else {
    png_byte buf[NEAR_BUF_SIZE];
    png_size_t read, remaining, err;
    check = 0;
    remaining = length;
    do {
      read = MIN( NEAR_BUF_SIZE, remaining );
      #if defined(_WIN32_WCE)
      if( !ReadFile( ( HANDLE )( io_ptr ), buf, read, &err, NULL ) ) {
        err = 0;
      }
      #else
      err = fread( buf, ( png_size_t )1, read, io_ptr );
      #endif
      png_memcpy( data, buf, read ); /* copy far buffer to near buffer */
      if( err != read ) {
        break;
      } else
      { check += err; }
      data += read;
      remaining -= read;
    } while( remaining != 0 );
  }
  if( ( png_uint_32 )check != ( png_uint_32 )length ) {
    png_error( png_ptr, "read Error" );
  }
}
#endif
#endif

/* This function allows the application to supply a new input function
  for libpng if standard C streams aren't being used.

  This function takes as its arguments:
  png_ptr      - pointer to a png input data structure
  io_ptr       - pointer to user supplied structure containing info about
  the input functions.  May be NULL.
  read_data_fn - pointer to a new input function that takes as its
  arguments a pointer to a png_struct, a pointer to
  a location where input data can be stored, and a 32-bit
  unsigned int that is the number of bytes to be read.
  To exit and output any fatal error messages the new write
  function should call png_error(png_ptr, "Error msg"). */
void PNGAPI
png_set_read_fn( png_structp png_ptr, png_voidp io_ptr,
                 png_rw_ptr read_data_fn ) {
  png_ptr->io_ptr = io_ptr;
  #if !defined(PNG_NO_STDIO)
  if( read_data_fn != NULL ) {
    png_ptr->read_data_fn = read_data_fn;
  } else
  { png_ptr->read_data_fn = png_default_read_data; }
  #else
  png_ptr->read_data_fn = read_data_fn;
  #endif
  /* It is an error to write to a read device */
  if( png_ptr->write_data_fn != NULL ) {
    png_ptr->write_data_fn = NULL;
    png_warning( png_ptr,
                 "It's an error to set both read_data_fn and write_data_fn in the " );
    png_warning( png_ptr,
                 "same structure.  Resetting write_data_fn to NULL." );
  }
  #if defined(PNG_WRITE_FLUSH_SUPPORTED)
  png_ptr->output_flush_fn = NULL;
  #endif
}
